unit 3 control!. iii. control of microorganisms: some definitions __________: greek for decay or...
TRANSCRIPT
Unit 3
Control!
III. CONTROL OF MICROORGANISMS: Some definitions
• __________: Greek for decay or putrid: bacterial contamination as in “septic tank”
• __________: (a) without infection; (b) free of infectious agents – Aseptic techniques in our lab
More Definitions to know! (table 7.1)
Make sure you know these terms and definitons!
Cidal versus static action• -cide or -cidal refers to killing (germicide,
tuberculocidal, fungicide etc)
• -stasis or –static or stat refers to inhibition without killing (fungistatic; bacteriostatic, etc)
• many important control methods are static rather than cidal
Cidal vs Static action
cidal static
Logarithmic death rate• upon exposure to a lethal agent organisms DO
NOT all die at the same time; they die at a logarithmic rate
• the same percentage of survivors dies during each equal time period
• sterility is achieved when number of survivors is less than one (could not have 0.2 survivor)
• effect of degreeof contamination
• (contamination = load)
Effect ofspore formationon deathrate.
Control Methods: Physical vs Chemical
• First physical control method (heat):
1. Moist heat
• a. Boiling: 100°C at sea level
• disinfection (cannot be relied upon to kill spores)
• Thermal death time at 100°C:Bacillus subtilis: 15-20 min.Clostridium botulinum: 360 min.Bacillus coagulans: 1140 min.
1. Moist heat
• a. Flowing steam: 100°C at sea level
• “instrument sterilizer”
• disinfection: does same as boiling
1. Moist heat
• b. Steam under pressure– function of pressure is to raise boiling point of water:
0 psi = 100°C5 psi = 110°C15 psi = 121°C30 psi = 135°C
• steam under pressure used for sterilization: should kill spores, viruses, etc– 1. _____ treatment of milk (ultra high temperature):
140°C for 4 sec (STERILIZATION)– Fruit Juice, Cream, Soy Milk, Yogurt, Wine– Malliard browning
2. Steam Autoclave
2. Pasteurization
• minimum 72°C for 15 seconds (_____)(75° if sugar in product); higher temps often used (Milk)
• should remove all pathogens• allowing only organisms that can withstand
heat to survive:– Streptococcus lactis– Lactobacillus spp.– some Bacillus species.
Louis Pasteur
3. Dry heat
• Direct Flaming: sterilization
• Incineration: sterilization
• Hot air oven: sterilizationcommon run: 170°C (350°F) for about 2 hours– dry heat requires longer times because for same
temp, it carries less heat.
Filtration
– physical removal of organisms from liquids– does not generally harm the organisms.
• e.g. can filter beer as alternative to pasteurization; filtration is important in water treatment
– can get filters with specific pore sizes– most filters pass viruses; a few remove them – millipore filter:
Millipore membrane filter
Filtration under pressure of vaccuum
Cold
• ______ for most organisms– Listeriosis is an exception that can still grow in
refrigerator
• refrigeration: optimum temp is just above freezing
• freezing: optimum temp for home freezer is 0°F (-17°C)
Drying (Desiccation)
• static for most organisms
• e.g. drying fruits, salted fish and meats as method of preservation
• lyophilization = freeze-vacuum drying– freeze item– dehydrate in powerful vacuum– static for most microorganisms– commonly used as a method of preserving
microbial cultures.– Static
The Electromagnetic SpectrumRadiation = Light
• a continuum of energy forms of different wave lengths
Ionizing Non-ionizing
The electromagnetic spectrum: effective wave lengths:
• a. ultraviolet radiation– damages DNA
– optimum wave length: 260 nm– Cidal, but poor penetrating ability
effect of ionizing radiation
Cidal = Can Result in Sterilzation, penetrates well but takes time…results in formation of free radicals
How about microwaves?
• Is yours a sterile environment ???
• Static for most bacteria
• Mositure containing foods Cidal for vegetative cells